Epitaxial integration of (0001) $BiFeO3$ with (0001) GaN

Epitaxial growth of (0001)-oriented $BiFeO3$ thin films on the (0001) surface of GaN has been realized using intervening epitaxial (111) $SrTiO3∕(100)$ $TiO2$ buffer layers. The epitaxial $BiFeO3$ thin films have two in-plane orientations: $[112¯0]BiFeO3‖[112¯0]GaN$ plus a twin variant related by a 180° in-plane rotation. $BiFeO3$ shows an out-of-plane remanent polarization of $∼90μC∕cm2$⁠, which is comparable to the remanent polarization of $BiFeO3$ prepared on (111) $SrTiO3$ single crystal substrates. The orientation of $BiFeO3$ realized on GaN provides the maximal out-of-plane polarization of $BiFeO3$⁠, which is equivalent to a surface charge of $5×1014electrons∕cm2$⁠.